STEP 1: Simulations
STEP home Simulations Data Mailing List

The first STEP project analysed two sets of sheared image simulations. These simulations were analysed by many different researchers with several different cosmic shear measurement methods. A report into the results of this analysis can be found here.

Set 1: SkyMaker simulations from Ludovic Van Waerbeke.
Set 2: Shapelet simulations from Richard Massey.

Both sets of simulations have a constant shear across them and a rather nasty set of PSFs. Please feel free to use these simulations to optimise your cosmic shear pipelines, including acknowledgements to Ludovic Van Waerbeke and/or Richard Massey in any publications.

Images generated using SkyMaker:

Images generated using Shapelets

  • Richard has produced simulations which can be downloaded here from
  • All the information you need about the simulations can be found here.

Rules for the analysis

  • All simulations have constant shear and constant PSFs. The SkyMaker simulations also have the same set of galaxies.
  • These measures have been taken to speed up the production of the simulations and also to simplify the final comparison analysis. Knowing that the simulations have these properties is however very different to what one would know about a real data set!
  • Therefore, please do not use extra information about the properties of each image simulation in your analysis and run your pipelines as you would normally on a set of real data.
  • Anisotropic PSF modelling should be performed on each simulation image . In the case of the SkyMaker simulations, PSFs should not be determined from a composite catalogue of stars in simulations with the same PSFs. Isotropy of the PSF across the image should not be assumed.
  • Galaxy positions should be determined from each simulation image with your normal source detection software, not from a composite catalogue.

Last modified 6th December.
STEP pages maintained by Catherine Heymans: heymans[at]